A switching network of this type has been disclosed in commonly owned U.S. Pat. No. 4,081,611. According to the disclosure of that prior patent, two such networks operate in parallel under the control of an associated processor designating one of them as a master and the other as a slave. The slave network, acting as a standby, provides the redundancy necessary to maintain existing connections in the event of a malfunction affecting the master network. The processor is also subdivided into two sections operating in such a master/slave relationship.
The need for letting the slave network take over the role of the master is determined by test circuits or malfunction detectors which, in the system of that prior patent, are part of a coordinating unit connected between outputs of the two switching networks. Such malfunction detectors can also be part of a centralized control unit; see, for example, Castriotta et al U.S. Pat. No. 4,208,552 which discloses a preprocessor coacting with a microprocessor in monitoring the correct operation of associated equipment. The centralized control unit constitutes a higher-ranking component of a hierarchical structure.
The replacement of a centralized control unit with interacting lower-ranking units in a nonhierarchical structure is also known in the art. See, for example, a papaer by R. Galimberti et al titled "Proteo System: An Overview", delivered at the International Switching Symposium of September 1981 in Montreal, Canada.